The terrorist behind last week’s Westminster attack was investigated as part of a plot to blow up an army base with a remote-controlled car.

Khalid Masood was probed six years ago over a possible connection to four Al Qaeda terrorists, the Telegraphclaims.

Luton-based Islamists Zahid Iqbal, Mohammed Sharfaraz Ahmed, Syed Hussain and Umar Arshad, were jailed for a total of 44 years in 2013 after admitting a plot to attack a Territorial Army base in their hometown.

Khalid Masood lived just a few hundred yards from one of the men, and is thought to have come into contact with them while they were attending a local gym.

Prime Minister Theresa May confirmed Masood had been investigated by security services for links to “violent extremism”, however it was decided he did not pose a direct threat.

The claim comes amid reports Masood was exposed to the teachings on notorious hate preacher Anjem Choudary, picking up extremist literature from a stall run by Al-Muhajiroun, an extremist group now banned in the United Kingdom.

The Timesreports that at least three former Al-Muhajiroun members lived near Britannia House, where Masood worked as an English teacher.

Farasat Latif, a former director of the school, told the paper Masood asked about the group.

“He asked me because he’s a new Muslim. He was like, ‘Who are these guys?’ We told him they are extremists who totally distort the teachings of Islam. He said, ‘Yup, fine’. I think he probably went to their stall and picked up a leaflet. I don’t think he went to their meetings.”

Mr Latif said he was surprised to learn Masood was behind the Westminster attack.

“He was apolitical. I have known a number of people move from mainstream to radical Islam — you see it in the way they talk. Violent radicals have a particular discourse of global jihad and politics — he did not have any of that at all. He never talked about the state of the Muslim world.”

“He told me that basically he’d had a troubled, violent past and he’d been in prison,” Mr Latif added. “That’s when he embraced Islam, that’s when he got solace and resolved to change his life.”